DESCRIPTION (From the Applicant's Abstract): The long-term goal of this research is to understand the genetic basis of development in the mesencephalon (midbrain) and metencephalon (anterior hindbrain) region (MMR) of the brain. Pattern formation throughout the MMR is directed by the coordinated activity of the glycoproteins Wntl and Fgf8, which are secreted by cells within the isthmic organizer (IsO). The IsO is the key signaling center in MMR development yet the molecular mechanism of its action is poorly understood. Two of the most important questions are i) "how are the genes encoding Wntl and FGF8 regulated?" and ii) "what are their distinct roles in IsO patterning?" Fgf8 signaling in known to rely on the transcription factors Enl, En2, Pax2 and Pax5 and at least part of their function is to participate in an autoregulatory loop. Understanding whether they govern Wntl expression independent of Fgf8 is crucial but unknown. In contrast, our research identified a unique transcription factor, Lmxlb, as being a key regulator of Wntl, and suggested that neither Wntl nor Lmxlb are part of the proposed Fgf8/Pax/En autoregulatory pathway. Nevertheless, some form of interplay exists between these signaling pathways because Wntl and Fgf8 expression are codependent. We propose to perform genetic experiments using both chick and zebrafish model systems to dissect the mechanisms that govern Wntl and Fgf8 expression. Our specific aims are: 1. To determine whether Lmxlb/Wntl activity ever impinges on En/Pax/Fgf8 expression. 2. To determine whether Pax2 or Pax5 ever i) directly maintain the Lmxlb/Wntl pathway or ii) act as cofactors for Lmxlb maintenance of Wntl . 3. To determine whether Enl or En2 directly maintain the Lmxlb/Wntl pathway. These studies should allow us to construct a model describing the coordinate regulation of Wntl and Fgf8. This should give insight into how early mammalian development occurs and eventually suggest means of preventing or treating human birth defects.